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Raman and surface-enhanced Raman spectra have been obtained for poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), a polymer blend widely used as a semitransparent, hole-transporting electrode coating in organic polymer-based photovoltaic cells. Spectra of thin films are reported for both the as-received (oxidized or doped) PEDOT:PSS and samples in which the PEDOT has been chemically reduced with hydrazine. The Raman spectra of the polymer blend are dominated by lines attributable to PEDOT and the oxidized and reduced species have clearly distinct Raman spectra at excitation wavelengths of 457.9, 514.5, and 632.8 nm. The Raman spectra in the ring stretching region exhibit changes in the presence of Au or Ag which depend on the method of deposition of the nanoparticles. Ag nanoparticles appear to facilitate reoxidation of chemically reduced PEDOT. Light-induced changes in the Raman spectra in the presence of Ag nanoparticles are consistent with addition of oxygen to the sulfur atoms in the thiophene rings of PEDOT. These results are discussed in the context of the reported enhancement of organic solar cell performance when metal nanoparticles are incorporated into or are in contact with the PEDOT:PSS layer.
Stavytska-Barba et al. (Fri,) studied this question.